51 research outputs found
The Hard-Constraint PINNs for Interface Optimal Control Problems
We show that the physics-informed neural networks (PINNs), in combination
with some recently developed discontinuity capturing neural networks, can be
applied to solve optimal control problems subject to partial differential
equations (PDEs) with interfaces and some control constraints. The resulting
algorithm is mesh-free and scalable to different PDEs, and it ensures the
control constraints rigorously. Since the boundary and interface conditions, as
well as the PDEs, are all treated as soft constraints by lumping them into a
weighted loss function, it is necessary to learn them simultaneously and there
is no guarantee that the boundary and interface conditions can be satisfied
exactly. This immediately causes difficulties in tuning the weights in the
corresponding loss function and training the neural networks. To tackle these
difficulties and guarantee the numerical accuracy, we propose to impose the
boundary and interface conditions as hard constraints in PINNs by developing a
novel neural network architecture. The resulting hard-constraint PINNs approach
guarantees that both the boundary and interface conditions can be satisfied
exactly and they are decoupled from the learning of the PDEs. Its efficiency is
promisingly validated by some elliptic and parabolic interface optimal control
problems
Variation of Critical Crystallization Pressure for the Formation of Square Ice in Graphene Nanocapillaries
Two-dimensional square ice in graphene nanocapillaries at room temperature is
a fascinating phenomenon and has been confirmed experimentally. Instead of
temperature for bulk ice, the high van der Waals pressure becomes an
all-important factor to induce the formation of square ice and needs to be
studied further. By all-atom molecular dynamics simulations of water confined
between two parallel graphene sheets, which are changed in size (the length and
the width of the graphene sheets) over a wide range, we find that the critical
crystallization pressure for the formation of square ice in nanocapillary
strongly depends on the size of the graphene sheet. The critical
crystallization pressure slowly decreases as the graphene size increases,
converging to approximately macroscopic crystallization pressure. The
unfreezable threshold for graphene size is obtained by estimating the actual
pressure and it is difficult to form the square ice spontaneously in practice
when the graphene sheet is smaller than the threshold. Moreover, the critical
crystallization pressure fluctuates when the graphene size is minuscule, and
the range of oscillation narrows as the sheet size increases, converging to the
macroscopic behavior of a single critical icing pressure for large sheets. The
graphene size also affects the stability and crystallization time of square
ice.Comment: 11 pages, 6 figure
A Comprehensive Review of One-Dimensional Metal-Oxide Nanostructure Photodetectors
One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years. Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates. Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities. This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field. It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO2, Cu2O, Ga2O3, Fe2O3, In2O3, CdO, CeO2, and their photoresponses. The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials. Finally, the review is concluded with some perspectives and outlook on the future developments in this area
Vitamin D and cause-specific vascular disease and mortality:a Mendelian randomisation study involving 99,012 Chinese and 106,911 European adults
Multiwalled Carbon Nanotube-TiO2 Nanocomposite for Visible-Light-Induced Photocatalytic Hydrogen Evolution
Multiwalled carbon nanotube- (MWCNT-) TiO2 nanocomposite was synthesized via hydrothermal process and characterized by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, field emission scanning electron microscope, thermogravimetry analysis, and N2 adsorption-desorption isotherms. Appropriate pretreatment on MWCNTs could generate oxygen-containing groups, which is beneficial for forming intimate contact between MWCNTs and TiO2 and leads to a higher thermal stability of MWCNT-TiO2 nanocomposite. Modification with MWCNTs can extend the visible-light absorption of TiO2. 5 wt% MWCNT-TiO2 derived from hydrothermal treatment at 140°C exhibiting the highest hydrogen generation rate of 15.1 μmol·h−1 under visible-light irradiation and a wide photoresponse range from 350 to 475 nm with moderate quantum efficiency (4.4% at 420 nm and 3.7% at 475 nm). The above experimental results indicate that the MWCNT-TiO2 nanocomposite is a promising photocatalyst with good stability and visible-light-induced photoactivity
Vapor-phase synthesis of one-dimensional ZnS, CdS, and ZnxCd1–xS nanostructures
One-dimensional (1D) nanostructures have received prime attention due to their high potential in understanding fundamental physical concepts and constructing nanoscale electronic devices. ZnS and CdS, the well-known direct and wide bandgap semiconductors, have recently attracted significant research interest due to their special properties and applications in sensing, optoelectronics, piezoelectronics, and lasing. This article reviews the most recent activities in ZnS and CdS nanostructures, with an emphasis on the authors' own results, and on 1D ZnS and CdS nanostructures, especially those synthesized using vapor deposition techniques. The review begins with a survey of ZnS and CdS nanostructures, and then is primarily focused on their 1D nanostructures, syntheses, characterizations, formation mechanisms, and optical and field-emission (FE) properties. Additionally, developments of ZnxCd1-xS composite nanostructures, including nanocombs and zigzag nanowires, are also discussed. Finally, we conclude this review with the perspectives and outlook on the future developments in this field.No Full Tex
One-dimensional nanostructures in porous anodic alumina membranes
We provide a brief summary of one-dimensional (1D) nanostructures, e.g., nanowires, nanotubes and hierarchical nanoarchitectures, synthesized in porous anodic alumina membrane (AAM) templates. After a brief introduction of fabrication process of AAMs with different pore sizes, various materials, namely, metals, compounds or alloys, organic nanowires/nanotubes, and hierarchical nanostructures prepared in AAMs are reviewed. The fabrication methods, including electrochemical deposition, surface sol-gel, modified chemical vapor deposition, atomic layer deposition, and layer-by-layer growth are then described. Finally, this review is concluded with an outline of some prospective directions regarding AAM-based nanostructures. Such nanostructures are ideal systems for the exploration of a large number of novel phenomena at the nanoscale and investigation of size and dimensionality dependence of nanostructure properties towards potential applications.No Full Tex
Polystyrene sphere-assisted one-dimensional nanostructure arrays: synthesis and applications
PET-RAFT Polymerization Catalyzed by Small Organic Molecule under Green Light Irradiation
Photocatalyzed polymerization using organic molecules as catalysts has attracted broad interest because of its easy operation in ambient environments and low toxicity compared with metallic catalysts. In this work, we reported that 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) can act as an efficient photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization under green light irradiation. Well-defined (co)polymers can be obtained using this technique without any additional additives like noble metals and electron donors or acceptors. The living characteristics of polymerization were verified by kinetic study and the narrow dispersity (Đ) of the produced polymer. Excellent chain-end fidelity was demonstrated through chain extension as well. In addition, this technique showed great potential for various RAFT agents and monomers including acrylates and acrylamides
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